An optical add-drop multiplexer (OADM) node comprises a collection of optical and control devices used in wavelength-division multiplexing systems for multiplexing and routing different channels of light into or out of, e.g., a single mode fiber (SMF). The terms “add” and “drop” in the context of an OADM node refer to the capability of the OADM node to add one or more new wavelengths, channels or colors to an existing multi-wavelength wavelength division multiplexed (WDM) or dense WDM (DWDM) signal, and/or to drop (remove) one or more channels, and thereby pass those signals to another network path. Thus, an OADM node may be considered to be a specific type of optical cross-connect.
A reconfigurable OADM (ROADM) node is a form of OADM node that adds the ability to remotely, via software control, switch traffic in a DWDM system (whereas OADM nodes are considered to have fixed add/drop capabilities with respect to, e.g., colors or direction). While there are several different technologies used to implement a ROADM node, such as microelectonic minors and planar lightwave circuits that may be employed to selectively route wavelengths from one port to another, a ROADM node provides certain basic functionality. Namely, a ROADM node enables flexible network transport by allowing add/drop of any channel. That is, a ROADM node allows for very flexible, remote selection and routing of wavelengths transiting a given node on a fiber network. A ROADM node may allow access to any of the wavelengths going through the node for use of the data on the chosen wavelength and the possibility of adding to, or modifying, the data on that wavelength for transmitting it on to the next node(s). A ROADM node also allows the interconnection of multiple intersecting networks (multiple degree nodes) at the optical level, avoiding the expense and complexity of optical-electrical-optical conversions to achieve the interconnection. Thus, as the demand in a given network changes, additional channels can be dropped or added, remotely via software control, creating a flexible provisioning system.